1. Field of the Invention
The present invention relates generally to the production of synthetic crimped fiber. More specifically, the present invention relates to a self-aligning, self-adjusting controlled discharge crimper, the method of operation thereof, and the fiber produced thereby.
2. Description of the Related Art
Synthetic textile fibers and cellulose acetate tow are typically manufactured from a continuous, multifilament bundle of fibers, which has been crimped using stuffer box crimper technology. FIG. 1 is a side view of a conventional stuffer box crimper. This device was first described in U.S. Pat. No. 3,120,692. A pair of driven feed rollers 1 deliver a multifilament band of uncrimped tow 2. A pair of scrapers 3 are fitted very close to the feed rollers 1 so as to prevent tow 2 from entering between the rollers 1 and the scrapers 3. Cheek plates (not shown in FIG. 1) are provided on either side of the feed rollers 1 and the scrapers 3 and fitted closely adjacent thereto. The cheek plates, together with the scrapers 3, form a crimping chamber. Moving fiber 2 is frictionally constrained within the chamber with a clapper 4. Air pressure biases the clapper 4 in a direction that closes the chamber. The fiber bends and buckles within the chamber causing the fiber to crimp. The crimped fiber applies pressure to the clapper 4 opposing the biasing force for the air pressure. As more fiber builds up in the chamber, the pressure increases. After some threshold, the clapper 4 opens allowing fiber to exit the chamber. The crimped fiber builds up quickly within the chamber. The resulting quick opening and closing of the clapper 4 causes a chattering effect.
The diameter of the fibers being crimped is frequently less than 0.0008 inches, and it is very easy for the fibers to catch between the driven feed rollers 1 and the scrapers 3. To prevent this from occurring, the scrapers 3 must be precisely positioned at a minimum space from the driven feed rollers 1. Scrapers 3 are positioned manually, however, and significant time and know how are required to do the job properly.
Fiber 2 can also get caught between the cheek plates and the driven feed rollers 1. To prevent this from happening, the driven feed rollers 1 must be precisely aligned with one another so that the ends of the feed rollers 1 are in precisely the same plane. Aligning the feed rollers 1 of the conventional device also requires manual control. If the feed rollers 1 are not properly aligned, the cheek plates are not evenly supported against them. One side of each roll may experience excess friction and the other side may experience a loose fit. On the excess friction side heat and wear can be problematic. On the loose fit side, the fiber can get caught.
Crimped fiber purchasers have placed increased emphasis on crimp uniformity. With the device shown in FIG. 1, the amount of crimp is affected by the movement of the clapper 4. As the chamber fills with crimped fiber, the amount of crimp given to the fiber increases. When the force of the fiber in the chamber is sufficient to open the clapper 4, fiber is allowed to escape freely until clapper 4 closes. During the interim, while the clapper 4 is open, little or no crimp is being imparted to the fiber 2. Within the crimping chamber there is inadequate control of the ratio of fiber inlet velocity to fiber outlet velocity. This produces a fiber having inconsistent crimp.
A review of the prior art related to stuffer box crimpers indicates that since their inception, there has been little change in the basic operating principles of these devices, with the exception of minor mechanical modifications. This not only holds true for acetate tow crimping, but also for the crimping of textile fiber tows in general. For example, U.S. Pat. No. 4,521,944 describes a dowel aligned multiple crimper to improve alignment of crimper components. This crimper, however, does not deviate in basic operating principle from conventional stuffer box crimper designs.
U.S. Pat. Nos. 3,924,911; 4,019,788; 4,395,804; 4,589,173; 4,662,042; 4,807,337 and 5,105,513 describe various methods of reducing cheek plate wear through modified cheek plate mounting means as well as improved lubricating means.
U.S. Pat. Nos. 3,528,149; 3,859,695; 3,936,917; 4,270,252; 4,503,593; 4,547,934; 4,707,896 and 4,854,021 describe various modifications and means of controlling clapper gates, but again the basic principle of operation of the stuffer box crimper is not modified. U.S. Pat. No. 3,160,923 diverges from conventional stuffer box concepts in that it utilizes conveyer belts in place of clappers. However, this crimper would be unacceptable for crimping flat, multifilament tow bands since it utilizes a tubular crimping chamber that would only be acceptable for crimping individual yarn strands. The conveyer belts in this patent are also rigidly positioned and are described as converging toward each other to form a progressively tapered compacting zone. Such a converging compaction zone would be detrimental to flat, crimped, multifilament tow bands.
U.S. Pat. No. 3,798,718 also uses conveyer belts. However, these belts are placed parallel to the nip of the input feed rolls and perpendicular to the direction of the inlet fiber path. This type of arrangement could not be utilized to crimp flat, multifilament tow bands and would be useful only for crimping individual yarn strands.
U.S. Pat. No. 3,137,055 describes a stuffer box type of crimper for yarn or tow (but the device really appears to be designed for yarns) that uses a pair of wheels, which extend normal to the axes of the feed rolls and extend peripherally into the crimping chamber adjacent the bite of the feed rolls to form a constriction in the chamber for retarding to a controlled extent the passage of the mass of packed fibers, and thereby maintaining a controlled crimping pressure. Experience has shown that the use of driven wheels of this type are not optimal for controlling the discharge rate of tow because of slippage that occurs between the fiber and the wheels. Constricting wheels of this type also compact and distort the crimp whose improved uniformity is the object of the invention.
Accordingly, it is an object of the present invention to avoid manual alignment of scrapers with driven feed rollers.
It is a further object of the present invention to provide a device that has a constant ratio of inlet fiber velocity to outlet fiber velocity.
It is another object of the present invention to provide a very close scraper/feed roller fit.
It is yet another object of the present invention to produce synthetic fibers having improved crimp uniformity.
It is still another object of the present invention to provide a device that maintains alignment of feed rollers and other parts while minimizing manual manipulation.
These and other objects are accomplished by providing a crimper having a pair of feed rollers to supply fiber traveling therebetween. The feed rollers rotate at a first speed. A pair of outlet rollers receive fiber from the feed rollers and rotate at a second speed, slower than the first speed. A pair of side walls sandwich the feed rollers and the outlet rollers. A pair of floating scrapers are supported by and move with, the feed rollers, the outlet rollers and the side walls. Fluid is supplied to and ejected from the scrapers such that a fluid bearing is created at least between the scrapers and the feed rollers.
There are two pairs of outlet rollers with a belt rotating about each pair. For each pair, a first of the outlet rollers is adjacent to the scraper and a second of the outlet rollers is displaced from the scraper. A space between the two scrapers defines a crimping chamber. The first outlet rollers are moved toward and away from one another, thereby causing the crimping chamber to open and close.
To move the first outlet rollers, a hydraulic positioning unit selectively supplies fluid to opposite ends of each first outlet roller with the pressure of the fluid supplied to the opposite ends being equalized. Equalized hydraulic biasing force is also used to bias the first outlet rollers toward the scrapers and to bias the feed rollers toward one another and toward the scrapers. Fiber produced by this method and with this device has superior crimp uniformity.
A self-aligning mechanism correctly positions the feed rollers and the first and second outlet rollers about three mutually perpendicular axes. For the first outlet rollers, the self-aligning mechanism includes a pair of side walls sandwiching the first outlet rollers to position them along a first axis. For the second axis of the first outlet rollers there are a pair of pivotal bearings, two pairs of arms and a pair of biasing devices. Each arm has inner and outer ends and a central portion. The central portion of each pair of arms rotates about one of the pivotal bearings. The inner ends of each pair connect with one of the first outlet rollers to control the position of the first outlet roller along the second axis. Each biasing device is connected to the outer ends of one pair of arms. For the third axis of the first outlet rollers, there are a pair of air springs and two pairs of hydraulic cylinders. Each air spring is connected to one of the first outlet rollers. Each pair of hydraulic cylinders is connected to one of the first outlet rollers to selectively bias the first outlet roller against a force from one of the air springs, to thereby control the position of the first outlet roller along the third axis. Each pair of hydraulic cylinders is in fluid communication.
For the feed rollers, the self-aligning mechanism uses the pair of side walls to sandwich the feed rollers to position them along the first axis. For the second axis of the feed rollers, there are two pairs of hydraulic reference cylinders, each pair being connected to one of the feed rollers to control the position of the feed roller along the second axis. Each pair of hydraulic reference cylinders is in fluid communication. For the third axis of the feed rollers there are a pair of pivotal bearings, two pairs of loading arms and a pair of hydraulic loading cylinders. Each loading arm has first and second ends and a central portion. The central portions of each pair of loading arms rotate about one of the pivotal bearings. The first ends of each pair connect with one of the feed rollers to control the position of the feed roller along the third axis. Each hydraulic loading cylinder is connected to the second ends of one pair of loading arms.